1. Field of the Invention
The present invention relates to an ink ribbon feed mechanism of a thermal recording type printing apparatus such as a facsimile machine and the like, and more particularly, to an ink ribbon feed arrangement that equalizes a ribbon tension over an entire ink ribbon width.
2. Description of Related Art
In a facsimile apparatus which is one example of a thermal recording type printing apparatus, an ink ribbon for recording is placed in the path of travel of recording paper (generally, a plain paper). The ink ribbon is usually wound on a feed roll, and printing is performed while the ink ribbon is being taken up onto a take-up roll. The ink ribbon is held stretched between the feed roll and the take-up roll. The recording paper and a recording head are provided in confronting relation interposing therebetween the ink ribbon. With heating the recording head, the ink coated on the ink ribbon melts to be transferred onto the recording paper.
FIG. 14 is a plan view showing an ink ribbon feed mechanism used in a conventional facsimile apparatus. In FIG. 14, an ink ribbon 101 is wound on a feed roll 102, and the leading end of the ink ribbon 101 is wound on a take-up roll 103. The take-up roll 103 rotates in the direction of an arrow Y in the drawing. That is, the ink ribbon 101 advances in the direction of an arrow X in the drawing, while being taken up on the take-up roll 103. The feed roll 102 and the take-up roll 103 are both supported nearly horizontally in relation to a bottom plate (not shown) of the facsimile apparatus by support frames 106A and 106B extending perpendicularly from the bottom plate.
The take-up operation of the ink ribbon 101 is effected by a friction mechanism 105 which drives the take-up roll 103. The friction mechanism 105 has a driving gear 108 which meshes with a gear 107 coaxially mounted on one end (on the right side in FIG. 14) of a spindle 103A of the take-up roll 103. To this driving gear 108 a controlled driving force is imparted. With the rotation of the driving gear 108, the take-up roll 103 rotates in the direction of the arrow Y, taking up the ink ribbon 101. However, if the rotational speed of the driving gear 108 is fixed, the amount of the ink ribbon 101 taken up on the take-up roll 103 increases (namely, the take-up roll 103 taking up the ink ribbon 101 becomes larger in diameter), increasing the take-up speed of the ink ribbon 101. There occurs, therefore, a difference in rotational speed between the take-up roll 103 and a platen roller (not shown) which carries recording paper. When a frictional force over a specific value is applied to the driving gear 108, or when the amount of the ink ribbon 101 wound on the take-up roll 103 has increased and a load to rotate the take-up roll 103 has increased over a specific value, idle rotation of the driving gear 108 occurs to absorb the speed difference from the platen roller. The other end (the left side in FIG. 14) of the take-up roll 103 is rotatably supported on a bearing section 109 provided on the support frame 106A, but no driving power is imparted to the other end of the take-up roll 103.
In the meantime, a back tension mechanism 104 is provided on the left end of the feed roll 102. The back tension mechanism 104 has a driving gear 112 which is meshed with a gear 111 coaxially mounted on one end (the left side in FIG. 14) of a spindle 102A of the feed roll 102. A specific driving power is given to the driving gear 112. The end of the feed roller 102 on the opposite side of the back tension mechanism 104 is only rotatably supported on a bearing 110 mounted on the support frame 106B, and is not imparted with the driving power.
With the impartment of the driving power to the driving gear 112, the back tension mechanism 104 gives a specific rotation force to the spindle 102A of the feed roll 102 in the direction of the arrow Z which is opposite to the direction of rotation Y of the take-up roll 103. Then, a force in the direction of feed (the direction of the arrow X) from the friction mechanism 105 and a force in the reverse direction (the opposite direction of the arrow X) of feed from the back tension mechanism 104 act on the ink ribbon 101.
As the friction mechanism 105 and the back tension mechanism 104 operate, the ink ribbon 101 is held with a fixed tension between the feed roll 102 and the take-up roll 103, thereby preventing the ink ribbon 101 from being broken and slacking.
In the conventional ink ribbon feed mechanism, however, the friction mechanism 105 and the back tension mechanism 104 are positioned on the opposite side in the direction of travel (the direction of the arrow X) of the ink ribbon 101. That is, as shown in FIG. 14, the friction mechanism 105 and the back tension mechanism 104 are arranged in diagonal positions of the wide ink ribbon 101. That is, in FIG. 14, the friction mechanism 105 is disposed on the right side, while the back tension mechanism 104 on the left side. Therefore, when the ink ribbon 101 is taken up, the driving power from the friction mechanism 105 for taking up the ink ribbon 101 and the driving power from the back tension mechanism 104 are on the opposite end of the ink ribbon 101. Thus, a twisting force occurs with the ink ribbon 101, producing a crease in the ink ribbon 101. A crease, if any in the ink ribbon 101, will deteriorate or unstabilize printing quality.
Furthermore, since the driving mechanism and the gear mechanism are disposed at opposite sides of the ink ribbon 101, the ink ribbon feed mechanism itself will increase in width. This has been a disturbance to space saving.
Further, the conventional ink ribbon feed mechanism includes a separation segment (not shown) provided between the recording head and the take-up roll 103 for separating the ink ribbon 101 from the recording sheet, the ink ribbon being pressed and heated at a position between the recording head and the platen roller for transferring an inked image onto the recording sheet. The separation segment is formed of a material, such as a resin, the same as that of a bottom side main body cover or a frame and is provided integrally therewith to enhance productivity. The separation segment has an elongated sliding surface extending in parallel with the rotation shaft 103A of the take-up roll 103. The sliding surface is positioned underneath and in contact with the ink ribbon to apply tension thereto, so that the ink ribbon can be separated from the recording sheet fed at an upper side of the ink ribbon. Accordingly, a combination of the friction mechanism 105, the back tension mechanism 104 and the separation segment will provide a given tension to the ink ribbon and separation effect of the ink ribbon from the recording sheet, to thus prevent the ink ribbon from being cut and slacking. Accordingly, it is desirable to provide a separation segment capable of providing a desirable tension of the ink ribbon.